Tensile support strength measurement system and method

ABSTRACT

A method and system determines probable strength degradation in a tensile support in an elevator system by monitoring an electrical characteristic of the tensile support as a whole, such as the total electrical resistance of the tensile support, that varies as the remaining strength in the tensile support varies. As the degradation of strength in a typical tensile support varies along the support, and as the relationship between strength and the electrical characteristic generally exhibits an inherent uncertainty, the overall relationship between strength and the electrical characteristic of the whole tensile support will vary as well. Quantifying the probable strength degradation indicated for each value in a range of a measurable electrical characteristic allows monitoring the strength degradation of the tensile support. The method and system also quantifies the relationship between tensile support degradation and a measurable electrical characteristic to monitor degradation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/589,479 filed Aug. 14, 2006, which is the national phase ofInternational application No. PCT/US04/08192 filed Mar. 16, 2004, nowU.S. Pat. No. 7,801,600, which issued Sep. 21, 2010.

TECHNICAL FIELD

The present invention relates to evaluating strength in a tensilesupport, and more particularly to a system and method that monitorstensile support strength based on electrical characteristics of thetensile support.

BACKGROUND OF THE INVENTION

Tensile supports, such as coated steel belts or wire ropes containingmetal cords, are used to move an elevator car up and down within anelevator shaft. Because the condition of the tensile support is criticalto safe operation of the elevator, there is a need to determine theremaining strength level of the tensile support and detect if theremaining strength level falls below a minimum threshold.

Tensile support strength can be reduced by normal operation of theelevator. The primary source of tensile support strength degradation isthe cyclic bending of the tensile support around sheaves as the elevatoris moved up and down in an elevator shaft. Tensile support degradationis normally not uniform along the length of the tensile support;instead, areas of the tensile support subjected to high levels orseverities of bending cycles will degrade faster than areas experiencingfewer bend cycles.

Some electrical characteristics, such as electrical resistance orimpedance, of the cords in the tensile support will vary as thecross-sectional area of the cords decrease. Thus, it is theoreticallypossible to determine the remaining support strength of the tensilesupport based on the cords' electrical characteristics. However, asnoted above, weaker spots in the tensile support are usually distributedover the tensile support in varying fashions depending on elevator usage(e.g., speed, acceleration, jerk, etc.), elevator system layout, thecord material, manufacturing variables, and other factors, making itdifficult to determine exactly when and where the tensile support mayhave reached its minimum remaining strength. Without a quantitativemethod relating an electrical characteristic of the tensile support withthe remaining tensile support strength, electrical monitoring of thetensile support can only reveal whether the tensile support is intact orbroken.

There is a desire for a system and method that can quantitativelyindicate a remaining strength level of cords in a tensile support basedon electrical characteristics of the cords, and therefore the electricalcharacteristic of the tensile support.

SUMMARY OF THE INVENTION

The present invention is directed to a method and system that candetermine strength degradation in a tensile support based on anelectrical characteristic, such as electrical resistance. One examplesystem determines a relationship between strength degradation andvarious physical factors, such as the rate of degradation for a givenload, operating environment information for the tensile support, andestimated or actual usage data, to obtain a map of mean degradation.This map of mean degradation is then used to generate one or more mapslinking the strength degradation (i.e., in the form of a remainingstrength percentage) and an electrical characteristic, such asresistance, that varies as the remaining tensile support strengthvaries. Based on these electrical characteristic maps, it is possible todetect when the tensile support has lost a given level of strength bymeasuring the electrical characteristic.

In one embodiment, variances in the degradation rate of the tensilesupport, the relationships between the electrical characteristic andstrength degradation, temperature, and/or electrical devices used tomeasure the electrical characteristic are taken into account to generatethe electrical characteristic maps.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a process for generating a map of meandegradation according to one embodiment of the invention;

FIG. 2 is a block diagram of a process for determining an apparentresistance according to one embodiment of the invention;

FIG. 3 is a plot of remaining strength probabilities for given increasesin apparent resistance according to one embodiment of the invention;

FIG. 4 is a plot of remaining strength probabilities for an estimatedusage and for an actual usage according to another embodiment of theinvention;

FIG. 5 is a block diagram illustrating one possible implementation ofthe invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As noted above, the strength of a tensile support is related to thecross-sectional area of the cords in the tensile support and accumulatedbreaks in the cords as the tensile support is bent and unbent around oneor more sheaves during elevator operation. Empirical testing can yield astrength loss model linking the loss in tensile support strength andelevator operation factors, such as tensile support loading, sheavegeometry (e.g., sheave diameter), and the number of bend cycles. Inother words, the model provides a relationship between a constant loadand the rate of strength degradation caused by the constant load.

Because different sections of the tensile support lose strength atdifferent rates, it is desirable to generate a map of mean degradationto predict the amount of strength degradation for any section in thetensile support. As a practical matter, it is virtually impossible tolocate the weakest portion of the tensile support directly. However,because weakened portions of the tensile support are distributed overthe entire tensile support length during use, the resistance of theentire tensile support can be an accurate indication of the weakestsection in the tensile support, which dictates the tensile support'sremaining strength.

FIG. 1 illustrates one method of generating the map of mean degradation100. In this embodiment, the map 100 is generated based on a strengthloss model 102 for the elevator system being considered, the elevatorconfiguration 104 and the estimated elevator traffic 106. Each of thesecomponents will be explained in greater detail below.

To obtain the strength loss model 102, the rate of degradation of thetensile support for a given constant load is obtained empirically. Inone embodiment, repeated bend cycles are applied to a plurality ofsample tensile supports until they break. This can be conducted usingany known fatigue machine. From this information, it is possible todetermine a statistical distribution of the number of bend cyclesrequired to bend a given tensile support to failure for a known constantload.

The remaining strength in the tensile support is also dictated by theelevator configuration 104, such as the number of sheaves in theelevator system, tensile support routing around the sheaves, thedistance between the sheaves, and the sheave configuration. Theestimated elevator traffic 106, such as frequency of use, averagepassenger weight, etc., is also considered in generating the meandegradation map. Usage details, such as the number of times the elevatormoves between certain floors, directly affects the location and amountof degradation in the tensile support. Taking estimated elevator traffic106 and the elevator configuration 104 into account keeps track of thenumber of times a sheave contacts a particular section of the tensilesupport and the tension at that time. This is tracked via a sheavecontact and load tracking algorithm 108. From this information, it ispossible to predict a wear state of a given section of the tensilesupport and therefore predict the remaining strength of the entiretensile support.

The mean degradation map 100 for a given elevator configuration 104 canbe analyzed statistically by varying the estimated elevator traffic data106 and the data on the degradation rate 102 and data 108 for monitoringthe effects of the load at areas where the sheave contacts the tensilesupport in different load and traffic situations. The resulting map ofmean degradation 100 provides a statistical distribution of strengthdegradation for a particular elevator system for a given constant load.In other words, the map of mean degradation 100 indicates a range ofbend cycles in which the tensile support is expected to fail for a typeof elevator system.

To detect remaining strength in the tensile support based on anelectrical characteristic, such as electrical resistance, theinformation in the map of mean degradation 100 needs to be linked withthe electrical characteristics of the tensile support, preferably in theform of electrical characteristic maps. FIG. 2 is a block diagramillustrating a process 200 according to one embodiment of the inventionto determine the relationship between electrical resistance andremaining strength.

To generate the electrical resistance maps in this embodiment, thedegradation map 100 is first considered with a degradation rate variance202, which reflects the uncertainty in the degradation rate reflected bythe map 100. Although the map of mean degradation 100 provides a rangeof possible values, the range itself reflected in the map 100 may alsovary. The degradation rate variance 202 takes this into account whendetermining the resistance maps. The amount of variance can bedetermined empirically.

Evaluating the degradation map 100 with respect to the degradation ratevariance 202 generates a range of usage patterns and wear rates of thetensile support and produces a range of minimum tensile support strengthand/or maximum loss in braking strength (LBS) 204, which reflects themaximum amount that the tensile support strength can be degraded. Moreparticularly, the maximum LBS can be determined by detecting the pointin the degradation map at which the tensile support strength is thelowest, after taking the degradation rate variance 202 into account, andthen using this point as the maximum LBS value 204. The maximum LBS 204indicates the point at which the tensile support would break if placedunder extreme load.

This maximum LBS 204 value that can be linked with an apparentresistance 205 value, which will be described in greater detail below.From this link, an operator can be alerted to a weak tensile supportcondition when the apparent resistance 205 reaches a value correspondingto the maximum LBS 204.

Note that linking the relationship between the resistance and the LBSfor multiple tensile supports only provides a range of possibleresistance values for the maximum LBS. Additional analysis, which willbe explained below, is needed to obtain the relationship betweenresistance values and strength characteristics other than the LBS.

As noted above, the loss in the cross-sectional area of the cords in thetensile support and accumulation of breaks in the cords may affectelectrical characteristics of the tensile support, such as increase theelectrical resistance. In the example shown in FIG. 2, a relationshipbetween the electrical resistance R and the LBS is developed empiricallyand analytically to generate an R vs. LBS map 206. Because therelationship between the resistance R and the LBS can vary randomlyamong tensile supports due to uncontrollable factors, such asmanufacturing variables and differing material properties, the process200 simulates these random variations in a variation map 208 and addsthem to the R vs. LBS map 206.

The modified degradation map 100, 202 and the modified R vs. LBS map206, 208 are incorporated together to generate an electrical resistancemap 210, which reflects the electrical resistance at any given sectionof the tensile support. As shown in the Figure, corresponding map pointsin the modified degradation map 100, 202 and the modified R vs. LBS map206, 208 are multiplied together to obtain the resistance map 210. Thetotal resistance of the tensile support at any given time can becalculated by summing 212 the resistances of the tensile supportsections together.

Temperature changes and variations among electronic devices in theelevator system may change the apparent resistance of the tensilesupport. In general, the effects of temperature-induced variances 214and electronic device variances 216 can be determined experimentallyand/or analytically. For example, the effect of temperature changes onthe tensile support resistance can be calculated as well as empiricallymeasured, while variances in electronic devices can be empiricallydetermined through testing. The process 200 incorporates the effects oftemperature-induced variance 214 and electronic device variances 216 onthe resistance value to generate a resistance map that reflects thepossible values of the apparent resistance 205. Alternatively, if thetemperature along the tensile support is known or simulated, thetemperature variance may be applied to each value in the resistance map210 before the summation 212 is performed.

Thus, the analysis shown in FIGS. 1 and 2 generates a distribution ofminimum remaining tensile support strength estimates and a correspondingdistribution of apparent resistances corresponding to the strengthestimates. These distributions can be analyzed statistically to produceprobability estimates of remaining tensile support strength for selectedelectrical resistances.

FIG. 3 is a graph illustrating one possible relationship between changesin the apparent, total tensile support resistance and the probabilityestimates of remaining tensile support strength. As shown in the Figure,the larger the percentage increase in the apparent resistance (shown inFIG. 3 as “DR”), the lower the amount of remaining strength in thetensile support. The distributions shown in FIG. 3 illustrate thepercentage of tensile supports having a given percentage of remainingstrength for a given percent increase in apparent resistance. From thisgraph, it is simple to estimate the amount of strength remaining in atensile support based on the amount its resistance has increased.

In another embodiment, the map of mean degradation 100 used to calculatethe apparent resistance and determine the strength probability map isbased on actual elevator usage data instead of simulated or historicaldata. To obtain this embodiment, actual elevator usage data can besubstituted for the estimated elevator traffic 106 in FIG. 1.

The actual elevator usage data may be continuously fed to the sheavecontact and load tracking algorithm 108 so that the map of meandegradation 100, and therefore the apparent resistance values 205 andcorresponding resistance maps, can be updated continuously as more dataregarding the elevator usage is obtained. In addition to the elevatorusage factors used to estimate tensile support degradation, thisembodiment also considers how the elevator is actually used and takespassenger loads and the severity and number of bend cycles in anysection of the tensile support into account. Because the strengthprobability estimates are based on actual elevator usage, the estimatesof the remaining strength levels obtained in this embodiment will likelyhave a narrower range than those in the first embodiment, whichencompasses a broad range of possible elevator usage.

FIG. 4 shows a comparison between an estimate of remaining tensilesupport strength based on estimated elevator usage versus actualelevator usage. The actual elevator usage data provides an electricalresistance value that improves the estimate of the remaining tensilesupport strength for a given elevator system, making it possible to setaction thresholds in an elevator health monitoring system that arerelevant to the particular elevator system being monitored.

FIG. 5 is a representative diagram of a system that evaluates tensilesupport strength as described above. Generally, the system 300 shouldinclude at least one electrical characteristic measurement device, suchas a resistance meter 302, that monitors the tensile support and atemperature measurement device 303 that monitors the tensile support'senvironment. The system 300 also includes a processor 304 that generatesthe maps described above from the measured electrical and temperaturecharacteristics and determines the probable remaining strength in thetensile support. The specific components to be used on the system 300can be selected by those of ordinary skill in the art.

By measuring the tensile support strength based on an electricalcharacteristic, such as electrical resistance, the invention can monitorthe remaining strength level of the tensile support, detect a minimumremaining strength level and, if desired, prompt action based on theremaining strength level. Although the examples described above focus ontensile supports used in elevator applications, such as coated steelbelts, the invention can be used to monitor the strength of anystructure whose electrical characteristics vary based on tensile supportstrength. Further, although the examples above focus on correlatingresistance with remaining strength, other electrical characteristics canbe monitored and used. The invention can be implemented in any knownmanner using any desired components; those of ordinary skill in the artwill be able to determine what devices are needed to obtain theelectrical characteristic data, obtain simulation data, and generateprograms that can carry out the invention in a processor, for example.

It should be understood that various alternatives to the embodiments ofthe invention described herein may be employed in practicing theinvention. It is intended that the following claims define the scope ofthe invention and that the method and apparatus within the scope ofthese claims and their equivalents be covered thereby.

1. A method of modeling a condition of an elevator tensile support,comprising; determining a rate of degradation of the tensile support fora selected load; modeling a configuration of at least one selectedelevator system; estimating an elevator traffic pattern; determiningsheave contact and load information using the determined rate ofdegradation, the modeled configuration and the estimated trafficpattern; and determining a mean degradation of the tensile support fromthe determined sheave contact and load information.
 2. The method ofclaim 1, including determining a plurality of mean degradation values byvarying at least one of the modeled configuration or the estimatedelevator traffic pattern.
 3. The method of claim 1, includingdetermining a relationship between an electrical characteristic and aselected condition of the tensile support and using the determinedrelationship and the determined mean degradation for determining anapparent electrical characteristic value corresponding to the selectedcondition of the tensile support.
 4. The method of claim 3, includingrepeatedly performing the steps of claim 3 to determine a plurality ofthe apparent electrical characteristic values and using the values todetermine a relationship between a corresponding measured electricalcharacteristic and a condition of a tensile support.
 5. The method ofclaim 4, wherein the electrical characteristic is resistance.
 6. Themethod of claim 5, including subsequently measuring a resistance of atensile support and using the determined relationship between resistanceand the selected condition of the tensile support to determine a currentcondition of the tensile support.
 7. The method of claim 1, includinggenerating a first map from the determined mean degradation; generatinga second map correlating an electrical characteristic with a selecteddegree of strength degradation; combining the first and second maps togenerate a third map correlating the electrical characteristic with theremaining strength in the tensile support.
 8. The method of claim 7,wherein the step of generating the first map comprises incorporating atleast one tensile support operational factor with the strength lossmodel.
 9. The method of claim 8, wherein said at least one tensilesupport operational factor is selected from the group consisting of anelevator system configuration, estimated elevator traffic, actualelevator usage, and sheave contact.
 10. The method of claim 9, whereinsaid at least one tensile support operational factor is the actualelevator usage, and wherein the step of generating the first map furthercomprises repeating the correlating step based on an updated actualelevator usage.
 11. The method of claim 7, wherein the combining stepcomprises: generating an intermediate map that correlates the electricalcharacteristic with remaining strength in a segment of the tensilesupport, wherein the tensile support comprises a plurality of segments;and summing the remaining strengths of the plurality of segments togenerate the third map.
 12. The method of claim 7, comprisingincorporating a degradation rate variance factor in the first map. 13.The method of claim 7, comprising incorporating an electricalcharacteristic variance factor in the second map.
 14. The method ofclaim 7, comprising incorporating at least one of a temperature-inducedvariance factor and an electronic device variance factor to generate thethird map.
 15. The method of claim 7, wherein the electricalcharacteristic is resistance.
 16. A system for determining a conditionof an elevator tensile support, comprising: a device for measuring anelectrical characteristic of at least a portion of the tensile support;and a controller that relates the measured characteristic to apredetermined data set indicating a relationship between correspondingapparent characteristic values and conditions of the tensile support anddetermines a current condition of the tensile support.
 17. The system ofclaim 16, wherein the controller determines a rate of degradation of thetensile support for a selected load; models a configuration of at leastone selected elevator system; estimates an elevator traffic pattern;determines sheave contact and load information using the determined rateof degradation, the modeled configuration and the estimated trafficpattern; and determines a mean degradation of the tensile support fromthe determined sheave contact and load information.
 18. The system ofclaim 17, wherein the controller determines a relationship between anelectrical characteristic and a selected condition of the tensilesupport and uses the determined relationship and the determined meandegradation for determining an apparent electrical characteristic valuecorresponding to the selected condition of the tensile support.
 19. Thesystem of claim 18, wherein the controller determines a plurality of theapparent electrical characteristic values and uses those values todetermine a relationship between a corresponding measured electricalcharacteristic and a condition of a tensile support.
 20. The system ofclaim 16, wherein the electrical characteristic is resistance.
 21. Acontroller useful for determining a condition of an elevator tensilesupport, comprising: programming for determining a rate of degradationof the tensile support for a selected load; modeling a configuration ofat least one selected elevator system; estimating an elevator trafficpattern; determining sheave contact and load information using thedetermined rate of degradation, the modeled configuration and theestimated traffic pattern; and determining a mean degradation of thetensile support from the determined sheave contact and load information.22. The controller of claim 21, including programming for determining aplurality of mean degradation values by varying at least one of themodeled configuration or the estimated elevator traffic pattern.
 23. Thecontroller of claim 21, including programming for determining arelationship between an electrical characteristic and a selectedcondition of the tensile support and using the determined relationshipand the determined mean degradation for determining an apparentelectrical characteristic value corresponding to the selected conditionof the tensile support.
 24. The controller of claim 23, includingprogramming for determining a plurality of the apparent electricalcharacteristic values and using the values to determine a relationshipbetween a corresponding measured electrical characteristic and acondition of a tensile support.